The Tile Calculator converts room area, tile size and grout gap into the number of tiles and boxes needed for a floor, wall or backsplash. Waste is added by layout pattern, since a diagonal or herringbone install wastes more material than a straight grid cut from the same tiles. A grout estimate and a negative-gap mode for overlapping material, such as roof tiles or wood siding, are both built in.
Calculate tile count from area and tile size
Tile count is the room's area divided by the footprint of a single tile including its grout joint, rounded up because a partial tile still consumes a whole one once it is cut. The calculator holds the room's length and width, the tile's length and width, and the gap between tiles as separate fields so each can be adjusted independently.
Tiles needed = Coverage area ÷ Tile footprint (rounded up)A 12-inch square tile and an 18-inch rectangular tile cover a floor at different rates even on the same room, and the grout gap changes the effective footprint of either one. Boxes are then calculated from the tile count and the number of tiles packed per box, which varies by product and is entered directly.
Set the grout gap or tile overlap
Grout gap sets the effective size of each tile once installed, since the tile itself is smaller than the space it occupies on the floor.
Rectified tile, cut to a precise, consistent edge, is typically laid with a gap as narrow as 1/16 inch, while a rustic or handmade tile with irregular edges needs a wider gap, sometimes up to 1/2 inch, to absorb that irregularity.
The gap field also accepts a negative value, which represents overlap rather than a joint. Roof shingles, wood siding and some metal panel products are installed with one piece overlapping the next rather than butted with a gap between them, and a negative gap reduces the effective tile footprint accordingly, increasing the number of pieces needed for the same area.
Apply the tile count formula
Effective tile size accounts for the grout gap on each side, and the room area is divided by that effective footprint rather than the tile's bare dimensions. Waste is added after the geometric count, and the final figure is rounded up since tile is sold whole.
Effective tile length = Tile length + Gap
Effective tile width = Tile width + Gap
Tile footprint = Effective length × Effective width
Tiles (geometric) = Room area ÷ Tile footprint
Tiles (with waste) = ROUND UP (Tiles geometric × (1 + waste%))A 1/16 inch grout gap changes a 12-inch tile's footprint only slightly, while a 1/2 inch gap on the same tile increases the footprint by a proportionally larger amount, since the gap applies to both the length and the width. That difference compounds over a large floor into a noticeably higher tile count for a wide grout joint versus a narrow one.
Estimate 12" tiles for a 20' × 15' floor
A 20 ft by 15 ft floor, tiled with 12-inch tiles at a 1/4-inch grout gap, needs 317 tiles laid in a straight grid. Every step below carries the units through. 1. Find the room area. 20 ft × 15 ft = 300 ft²
2. Find the effective tile size. 12 in + 0.25 in = 12.25 in = 1.0208 ft
3. Find the tile footprint. 1.0208 ft × 1.0208 ft = 1.0421 ft²
4. Divide area by footprint. 300 ft² ÷ 1.0421 ft² = 287.9 tiles (geometric)
5. Add 10 percent waste for a straight grid. 287.9 × 1.10 = 316.7, rounds up to 317 tiles
6. Convert to boxes at 10 tiles per box. 317 ÷ 10 = 31.7, rounds up to 32 boxes
Switching the same floor to a diagonal layout raises the waste allowance to 15 percent, pushing the tile count to 287.9 × 1.15 = 331 tiles, 14 more than the straight-grid figure for identical dimensions and tile size.
Add waste for layout and cuts
Layout pattern determines how much of each cut tile ends up unused, since a pattern that meets a wall at an angle wastes the offcut from every edge tile, while a square grid can often reuse an offcut on the opposite wall. The calculator sets a default waste percentage from the selected layout and leaves the figure editable.
| Layout | Waste |
|---|---|
| Straight grid | 10% |
| Running bond | 10% |
| Diagonal | 15% |
| Herringbone | 15% |
A straight grid and a running bond, where each row shifts by half a tile, waste material at similar rates because both cut tiles cleanly along the room's walls. Diagonal and herringbone patterns cut every edge tile at an angle, and that angled offcut is rarely large enough to reuse elsewhere on the same floor, which is why both carry a 50 percent higher default waste allowance than the two grid patterns.
Choose tile material by room
Tile material affects durability, water resistance and cost far more than it affects the count formula above, which stays identical regardless of material selected. Matching material to room reduces the chance of an early failure from moisture or wear the tile was never rated for.
Ceramic tile is the common choice for dry interior floors and walls, cost-effective and available in the widest range of sizes and finishes. Porcelain is denser and less porous than ceramic, standard for wet areas such as showers and bathroom floors, and for any exterior application. Glass tile is used mainly for backsplashes and accent walls rather than floors, since it scratches and chips more readily underfoot. Quarry tile, unglazed and highly durable, suits heavy-traffic commercial floors and mudrooms. Marble and granite are natural stone options, porous unless sealed, chosen for their appearance in bathrooms and kitchen surfaces where the extra maintenance is accepted for the finish.
Estimate grout quantity
Grout volume depends on the total length of joint between tiles, the width of the gap, and the depth of the joint, which is set by tile thickness. A wider gap or a thicker tile both increase the volume of grout a given floor consumes for identical tile counts.
Grout volume ≈ (Tile length + Tile width) × Gap × Tile thickness × Tile countFor the 20 ft by 15 ft floor above, using 12-inch tiles, a 0.25-inch gap, a 3/8-inch (0.375 in) tile thickness and 317 tiles: (12 + 12) × 0.25 × 0.375 × 317 = 713.25 in³, which converts to 0.413 ft³, or about 0.0117 m³. At a dry grout density of 1,600 kg/m³, that comes to roughly 18.7 kg, or about 41 lb, of dry grout mix before water is added. This is an estimate; actual consumption varies with mixing loss, joint depth variation and how tightly the tiles are laid, so buying slightly more than the estimate is standard practice.
Plan the layout pattern
Layout pattern is chosen before tile count is finalised, since pattern sets both the waste percentage and, for some patterns, a minimum tile size ratio. A linear grid runs tiles in straight rows and columns and is the simplest and lowest-waste option for a room with square corners.
Running bond staggers each row by roughly half a tile length, similar to a brick wall, and hides small size variations between tiles better than a strict grid does. Herringbone and diamond patterns run tiles at an angle to each other or to the room, both producing a more visually complex floor at the cost of a higher waste percentage. Herringbone in particular is usually laid with a rectangular tile at roughly a 2:1 length-to-width ratio, since that proportion is what produces the interlocking zigzag the pattern is named for. A 45-degree diagonal grid is a linear grid rotated relative to the walls rather than a distinct pattern, and it carries the same higher waste allowance as herringbone because every perimeter tile is cut at an angle.
Frequently asked questions
How many tiles do I need for 300 square feet?
It depends on tile size and grout gap. For 12-inch tiles at a 1/4-inch gap in a straight grid, 300 ft² needs about 317 tiles including a 10 percent waste allowance. Larger tiles reduce the count; a wider grout gap slightly increases it.
How much extra tile should I buy for waste?
Ten percent for a straight grid or running bond layout, and 15 percent for a diagonal or herringbone layout. Rooms with many corners, niches or a complex layout may need more than the default, since each additional cut edge adds another offcut that is rarely reusable.
What size gap should I leave between tiles?
As narrow as 1/16 inch for rectified tile with a precise, consistent edge, up to about 1/2 inch for a rustic or handmade tile with more size variation. The gap should be wide enough to absorb the tile's actual edge tolerance without looking uneven once grouted.
Can the tile gap be zero or negative?
Yes. A gap of zero represents tiles butted directly together with no visible joint. A negative gap represents overlap rather than a joint, used for products such as roof shingles or lap siding where one piece covers part of the next, which increases the number of pieces needed for a given area.
How much grout do I need for a tile floor?
Grout volume depends on the total joint length, the gap width and the tile thickness. A 300 ft² floor with 12-inch tiles, a 1/4-inch gap and 3/8-inch tile thickness needs roughly 18.7 kg, about 41 lb, of dry grout mix, before accounting for mixing loss.
What is the difference between ceramic and porcelain tile?
Porcelain is denser and less porous, making it suitable for wet areas and exterior use, while ceramic is more affordable and available in a wider range of styles for dry interior floors and walls. Both are counted and estimated identically by area, tile size and gap.
Which layout pattern wastes the most tile?
Diagonal and herringbone layouts carry the highest default waste allowance, at 15 percent, because every tile along the room's perimeter is cut at an angle and the offcut is rarely large enough to use elsewhere. Straight grid and running bond layouts default to 10 percent.
How do I calculate tile for a diagonal layout?
Use the same area and tile footprint calculation as a straight grid, then apply the higher 15 percent waste allowance instead of 10 percent. A 300 ft² room needing 287.9 tiles geometrically would need 331 tiles at the diagonal waste rate, compared with 317 at the straight-grid rate.
Does tile size affect the waste percentage?
Not directly. Waste percentage is set by layout pattern, not tile size, though larger tiles produce fewer total cuts across a given room, which can mean less total offcut material even at the same percentage. A room tiled in large-format tile typically wastes less material in absolute terms than the same room in small mosaic tile.
How many boxes of tile should I order?
Divide the total tile count, including waste, by the number of tiles packed per box, then round up. A 317-tile order at 10 tiles per box needs 32 boxes; buying a full box over the calculated minimum is standard practice in case of breakage or a miscount during installation.
Summary
The Tile Calculator converts room area and tile size into a tile count and box count, using the grout gap to set each tile's effective footprint and the layout pattern to set the waste allowance.
Straight grids and running bond default to 10 percent waste; diagonal and herringbone default to 15 percent because every edge tile is cut at an angle.
A grout estimate built from joint length, gap width and tile thickness adds a dry-mix weight to the same result, and a negative gap value covers overlapping products such as siding and roofing.